nearly every 2 weeks the slapd stops answering on search requests. The
process is still running(socket is open as well) but every questions
runs into a timeout.
When that happen, I need to kill the process with "-9" manually. After
that I can start the process again.

We have configured a Master(Read-Write)-Slave(Read-Only) cluster,
actually it happend on the Slave but it also had happend on the Master,
but not that often.
When the process on the Master crashes, the DB is broken and I need to
restore a backup via slapcat ...